Implement Flatten for DictArray

vortex-array/src/compute/flatten.rs

@@ -49,6 +49,16 @@ pub fn flatten(array: &dyn Array) -> VortexResult<FlattenedArray> {
     })
 }
 
+pub fn flatten_varbin(array: &dyn Array) -> VortexResult<VarBinArray> {
+    if let FlattenedArray::VarBin(vb) = flatten(array)? {
+        Ok(vb)
+    } else {
+        Err(VortexError::InvalidArgument(
+            format!("Cannot flatten array {} into varbin", array).into(),
+        ))
+    }
+}
+
 pub fn flatten_bool(array: &dyn Array) -> VortexResult<BoolArray> {
     if let FlattenedArray::Bool(b) = flatten(array)? {
         Ok(b)

vortex-dict/src/compute.rs

@@ -1,11 +1,21 @@
+use std::sync::Arc;
+
+use vortex::array::primitive::PrimitiveArray;
+use vortex::array::varbin::VarBinArray;
+use vortex::compute::flatten::{flatten, flatten_primitive, FlattenFn, FlattenedArray};
 use vortex::compute::scalar_at::{scalar_at, ScalarAtFn};
+use vortex::compute::take::take;
 use vortex::compute::ArrayCompute;
 use vortex::scalar::Scalar;
-use vortex_error::VortexResult;
+use vortex_error::{VortexError, VortexResult};
 
 use crate::DictArray;
 
 impl ArrayCompute for DictArray {
+    fn flatten(&self) -> Option<&dyn FlattenFn> {
+        Some(self)
+    }
+
     fn scalar_at(&self) -> Option<&dyn ScalarAtFn> {
         Some(self)
     }
@@ -17,3 +27,69 @@ impl ScalarAtFn for DictArray {
         scalar_at(self.values(), dict_index)
     }
 }
+
+impl FlattenFn for DictArray {
+    fn flatten(&self) -> VortexResult<FlattenedArray> {
+        let codes = flatten_primitive(self.codes())?;
+        let values = flatten(self.values())?;
+
+        match values {
+            FlattenedArray::Primitive(v) => take(&v, &codes).map(|r| {
+                FlattenedArray::Primitive(
+                    Arc::try_unwrap(r.into_any().downcast::<PrimitiveArray>().unwrap())
+                        .expect("Expected take on PrimitiveArray array to produce new array"),
+                )
+            }),
+            FlattenedArray::VarBin(vb) => take(&vb, &codes).map(|r| {
+                FlattenedArray::VarBin(
+                    Arc::try_unwrap(r.into_any().downcast::<VarBinArray>().unwrap())
+                        .expect("Expected take on VarBin array to produce new array"),
+                )
+            }),
+            _ => Err(VortexError::InvalidArgument(
+                "Only VarBin and Primitive values array are supported".into(),
+            )),
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use vortex::array::downcast::DowncastArrayBuiltin;
+    use vortex::array::primitive::PrimitiveArray;
+    use vortex::array::varbin::VarBinArray;
+    use vortex::array::Array;
+    use vortex::compute::flatten::{flatten_primitive, flatten_varbin};
+    use vortex_schema::{DType, Nullability};
+
+    use crate::{dict_encode_typed_primitive, dict_encode_varbin, DictArray};
+
+    #[test]
+    fn flatten_nullable_primitive() {
+        let reference =
+            PrimitiveArray::from_iter(vec![Some(42), Some(-9), None, Some(42), None, Some(-9)]);
+        let (codes, values) = dict_encode_typed_primitive::<i32>(&reference);
+        let dict = DictArray::new(codes.to_array(), values.to_array());
+        let flattened_dict = flatten_primitive(&dict).unwrap();
+        assert_eq!(flattened_dict.buffer(), reference.buffer());
+    }
+
+    #[test]
+    fn flatten_nullable_varbin() {
+        let reference = VarBinArray::from_iter(
+            vec![Some("a"), Some("b"), None, Some("a"), None, Some("b")],
+            DType::Utf8(Nullability::Nullable),
+        );
+        let (codes, values) = dict_encode_varbin(&reference);
+        let dict = DictArray::new(codes.to_array(), values.to_array());
+        let flattened_dict = flatten_varbin(&dict).unwrap();
+        assert_eq!(
+            flattened_dict.offsets().as_primitive().buffer(),
+            reference.offsets().as_primitive().buffer()
+        );
+        assert_eq!(
+            flattened_dict.bytes().as_primitive().buffer(),
+            reference.bytes().as_primitive().buffer()
+        );
+    }
+}